Java and Distributed Systems

Transcription

1 Java and Distributed Systems Dr. Stephan Fischer GMD-IPSI Dolivostr. 15 D Darmstadt

2 Contents Remote Method Invocation Java and CORBA Jini Discussion

3 Java RMI (1) RMI applications: Client/server architecture Client requests service which is executed transparently on server Typical server creates remote objects and offers them via references to client Client accesses objects by references RMI: Mechanisms for Client/server communication: Distributed applications/systems

4 Java RMI (2) Properties of distributed objects localization of objects application registers for remote object (RMIregistry) exchange references to remote objects communication with remote objects hidden from application by RMI appear like local calls class loading of remote objects

5 RMI functionality Java RMI (3) Client Registry Server Webserver Webserver

6 RMI: Architecture Java RMI (4) RMI server RMI client skeleton remote reference layer transport layer virtual link network link stubs remote reference layer transport layer

7 Skeletons Java RMI (5) server-side component interacting with server- RRL receive method call requests of client-rrl extract arguments and call server method accept return values and marshals them

8 Stub Java RMI (6) represents remote object at client side defines interfaces to support implementation of remote object is referenced like local objects client-side RRL passes stream (objects, arguments) to stub serializes parameter data and passes to stream deserializes received objects

9 Java RMI (7) Remote Reference Layer referencing protocol, independent from stub or skeleton models client-side: Server-specific information, passed to server-side RRL provides referencing semantics and processes data according to semantics before passing to skeleton for method call

10 Transport layer Java RMI (8)... manages links between client and server... realizes abstractions: endpoint: used to reference address space of VM channel: link between address spaces. Manages link between client and server link transport: channel establishment between local address space and remote end-point

11 Properties of RMI Java RMI (9) callback operations dynamic class loading remote interfaces, objects and methods object persistence object activation

12 Callback operations Java RMI (10) two-way communication between objects implementation of interface Remote to use object reference passed from one computer to another object export to be able to receive remote method calls (extending UnicastObject)

13 Java RMI (11) Callback: Example bank transaction client/server model: Client requests account value from server extended model: Client requests account value from server, server requests password correct answer only provided if password correct

14 Java RMI (12) Dynamic class loading RMI: System of distributed Java-to-Java applications migrate objects from address space 1 to address space 2 (different from CORBA!) transmit (static) data and (dynamic) behavior, as well as class definitions (serialization and RMI class loader) required: Implementation of interface Serializable

15 Java RMI (13) Remote interfaces, objects and methods remote object implements remote interface which extends java.rmi.remote each interface method contains java.rmi.remoteexception within throws-clause uses stub object to access remote object instead of local copy application calls local stub which calls remote skeleton

16 Object persistence Java RMI (14) remote method call requires object passing implementation of interfaces Serializable or Externalizable rules pass remote objects with a reference, realized as stub (client-side proxy) implementing remote interfaces which remote object implements pass local objects as copies (using serialization)

17 Object activation Java RMI (15) normally: Server generating object instance is running inside VM to obtain reference to remote object large-scale systems: Deactivate objects which are not needed, activate necessary objects RMI: Activation mechanism assign name to object by registry activate object later by referencing using registry advantage: Application which generates instances of remote object can terminate before object is needed. use RMI Actication System Daemon (rmid)

18 Object activation Java RMI (16) client requests object name using registry registry responds with remote reference which causes rmid call client calls remote method using rmid (not Registry!) using remote reference rmid passes call to instance of object implementation start rmid as background process: start rmid object: implement interface Activatable instead of UnicastObject

19 Java RMI (17) Distributed applications in RMI development and implementation of components of distributed application compilation of source files and generation of stubs creation of network connectivity of classes using WWW server start of application

20 Java RMI (18) Development and implementation of components of distributed application Architecture definition: Creation of local and remote components definition of remote interfaces implementation of remote objects implementation of clients

21 Java RMI (19) Compilation of source files and generation of stubs compilation of source files using javac implementation of remote interfaces, server and client classes compilation of new source files using rmic creation of stubs for remote objects

22 Start of application Java RMI (20) start of RMI registry for remote objects: rmiregistry mapping of object names to objects, resolving of external references start of server start of client

23 RMI Example (1) Application client calls remote service server accepts request and processes service server returns result to client

24 RMI Example (2) Definition of interface import java.rmi.*; public interface AccountUpdate extends Remote { } public int updateaccount(int number) throws RemoteException;

25 RMI Example (3) Implementation class import java.rmi.*; import java.rmi.server.*; import java.io.serializable; public class AccountUpdateImpl extends UnicastRemoteObject implements AccountUpdate, Serializable { public AccountUpdateImpl() throws RemoteException {} } public int updateaccount (int number) throws RemoteException { } //implemented later return 0;

26 RMI Example (4) Stub and skeleton classes (compilation of classes using javac) stub and skeleton classes access implementation classes rmic AccountUpdateImpl creates... AccountUpdateImpl_Skel.class AccountUpdateImpl_Stub.class

27 RMI Example (5) Server application import java import java.rmi.registry.*; public class Account{ public static void main (String args[]) { if (args.length!= 2) { } System.err.println("Call: java Account <Server> <Port>"); System.exit(1); String server = args[0]; int port = Integer.parseInt(args[1]);

28 RMI Example (6) //New Security Manager System.setSecurityManager(new RMISecurityManager()); try { //Location of Registry LocateRegistry.createRegistry(port); //Instance of Account application AccountUpdateImpl aui = new AccountUpdateImpl(); //Bind object instance to registry String urlstring = "//" + server + ":" + port + "/AccountUpdate";

29 RMI Example (7) } } // rebind Naming.rebind(urlString, aui); }catch (Exception e) { System.out.println("Error"); } e.printstacktrace(); System.out.println(e.getMessage());

30 RMI Example (8) Problem: RMI uses System.setSecurityManager file java.policy has to be extended: grant codebase "file:<directory>" {permission java.security.allpermissions; };

31 Client application import java.rmi.*; public class Client { RMI Example (9) public static void main (String args[]) { AccountUpdate au = null; if (args.length!= 2) { System.err.println("Eingabe: java Client <Server> <Port>"); System.exit(1); } String server = args[0]; int port = Integer.parseInt(args[1]);

32 RMI Example (10) //New Security Manager System.setSecurityManager(new RMISecurityManager()); try { //Binding of object instance to registry String url = "//" + server + ":" + port + "/AccountUpdate"; au = (AccountUpdate)Naming.lookup(url); } catch (Exception e) { System.err.println("No Connection"+e); }

33 RMI Example (11) } } try { //update account int result = au.updateaccount(10); } catch (Exception e) { } System.err.println("Error");

34 Java and CORBA (1) Common Object Request Broker Architecture framework for distributed systems to support heterogeneous architectures hardware (CPU, file system) operating system and programming language RMI: focuses on homogeneous architectures (both communication partners use Java) management of system resources providing different services

35 Java and CORBA (2) Object Management Group (OMG) consortium of engineers developing architecture to enable transparent cooperation of programming and operating system environments result of specifications: CORBA Object Request Broker (ORB): Heterogeneous object components can collaborate over networks and operating system borders interfaces to CORBA objects: Interface Definition Language (IDL)

36 Java and CORBA (3) CORBA and other programming languages CORBA objects can be at arbitrary locations within network cooperate with objects of other platforms can be implemented in various programming language. Constraints: Mapping from OMG-IDL to programming language necessary. Java, C, C++,...

37 Java and CORBA (4) Commercial CORBA Components implementation of ORB IDL compiler implementation of Common Object Services (COS, CORBAServices) application-dependent environments (CORBAFacilities) since CORBA2.0: Internet-Inter-ORB protocol (IIOP)

38 Java and CORBA (5) Object Request Broker (ORB) link objects of isolated address spaces use marshaling to bundle parameters, return values, and exceptions ORB Object Bus ORB Client Server

39 ORB examples Java and CORBA (6) ORB resident within client and object implementation server-based ORB system-based ORB runtime-library-based ORB

40 Java and CORBA (7) Common Object Services (COS) support ORB naming service event service security service transaction service

41 Java and CORBA (8) Application- Objects Common Facilities Vertical CORBA-Facilities Health Finance... Horizontal CORBA-Facilities User Interface Info Mgmt. System Mgmt. Task Mgmt. Object Request Brokers Lifecycle Naming Persistence CORBA-Services

42 Java and CORBA (9) Interface Definition Language (IDL) interface for ORB, COS, and Common Facilities describes neutral interface language for service implementations simple data types (basic values). Example: Short, Long complex data types (constructed values). Example: Struct, Sequence

43 Example module demo { }; Java and CORBA (10) interface text { }; readonly attribute string message; long connect (in long id);

44 Java and CORBA (11) Internet-Inter-ORB Protocol (CORBA2.0) Universal Networked Objects (UNO) using TCP/IP and General-Inter-ORB protocol (GIOP) GIOP defines communication of ORBs

45 Java and CORBA (12) UNO use interoperable message format: Common Data Representation (CDR) example: conversion IDL to network format, byte order difference to External Data Representation (XDR): Variable byte order for systems with same word format

46 Java and CORBA (13) Object-Request- Semantics IDL Transfer- and Message- Syntax CORBA- General-Inter-ORB- Protocol (GIOP) Environment-specific Inter-ORB- Protocols (ESIOP) DCE Transport Internet- Inter-ORB- Protocol (IIOP) OSI IPX/SPX DCE-RPC over UDP DCE-RPC over OSI TCP/IP IPX UDP X.25

47 Java and CORBA (14) Using CORBA: Steps design development object development using IDL interfaces, grouping to modules creation of stubs and skeletons using IDL compiler implementation of interfaces server start and object initialization using naming service

48 Java and CORBA (15) Client Server-Objects Dynamic Invocation Interface Objectadapter Client- IDL- Stubs ORB- Interface Static-IDL- Skeleton Dynamic Skeleton ORB Core - Transport Protocol Interface identic for all ORB-Implementations Up-call interface Many Object Adapters Stub and Skeleton for each object type Normal call interface

49 CORBA objects Java and CORBA (16) are described using IDL-file (definition of object type) IDL interface declares operations, exceptions, and type attributes (values) operation: Consists of signature (name, parameters, result, and exceptions)

50 Java and CORBA (17) Example: module AccountApp { interface AA { string hello(); }; }; idltojava: Creates package AccountApp, and interface AA.java within directory AccountApp

51 Java and CORBA (18) Stubs and skeletons extend common ORB class (object communication) use Naming Service to offer/retrieve information about object

52 Java and CORBA (19) Registration Request Naming Service Object Implementation Local Object Reference Skeleton Virtual Link Stub ORB-Class Server Network Link ORB-Class Client

53 CORBA Client Java and CORBA (20) Client-Program Language-Dependent Object References ORB-Object References Dynamic Invocation Interface Stubs for Interface A Stubs for Interface B

54 CORBA Server Java and CORBA (21) offers references to CORBA objects (Naming Services) transient objects persistent objects (ORB demon starts necessary server) Java IDL: exclusively transient objects

55 Java and CORBA (22) CORBA-Server (2) Object Implementation Methods for Interface A Object Data Upcall- Method Library-Routines ORB-Object References Skeleton for Interface A Dynamic Skeleton Objekt Adapter Routines

56 Java and CORBA (23) Object Adapter IDL-Declaration Stubs and Skeletons IDL-Compiler Source-Code Server Objects Portable Object Adapter Compiler Interface Repository Client-IDL Server-IDL Server Objects Stubs Skeletons Binaries Implementation Repository Client Server

57 Java IDL Java and CORBA (24) IDL file contains elements defining name space IDL declaration are case insensitive IDL does not support overloading and overwriting of operations, although (simple and multiple) heredity possible

58 Java and CORBA (25) IDL Modules definition of group of IDL interfaces nesting of modules possible translated to Java package example module App { interface AA { };» string hello(); };

59 IDL Interfaces Java and CORBA (26) contain attributes, exceptions, and operations attributes: Examples boolean (IDL): byte (Java) enum, struct (IDL): class (Java) long (IDL): int (Java) long long (IDL): long (Java) string (IDL): java.lang.string (Java) unsigned short (IDL): short (Java)

60 Java and CORBA (27) IDL interfaces: translation by idltojava interface class with same name as interface name implementation base class (skeleton code for server) stub class helper class (restrict object reference to stub object requested by client) holder class (reference to IDL interface object if interface passed as argument)

61 Java and CORBA (28) IDL attributes: Translation by idltojava creates getter and setter method readonly: omit setter method example IDL: attribute long zaehler; Java: int zaehler(); void zaehler(int arg);

62 Java and CORBA (29) IDL operations identifier in: call by value identifier out: call by reference (Java: class <JavaType>Holder to encapsulate data variable containing containing parameter. Passing of class reference) identifier inout: call by value and call by reference identifier raises: define exception handling

63 IDL Exceptions Java and CORBA (30) passed as object references extend class org.omg.corba.userexception example: exception PwdException { string reason; }; interface password { }; void getpassword(out string pwd) raises (PwdException)

64 IDL struct Java and CORBA (31) container class to group data example: struct Account { }; long number; long amount;

65 IDL typedef Java and CORBA (32) define new IDL types are not mapped directly to Java: IDL compiler replaces typedef with IDL type example: typedef string Password;

66 IDL sequence Java and CORBA (33) definition of one-dimensional arrays (bounded and intervals) marshaling: Check if array boundaries are OK if not: MARSHAL-exception create helper and holder class within Java example typedef sequence <string, 10> passwords;

67 IDL array Java and CORBA (34) bounded arrays example: typedef string passwords[10]; IDL enum enumeration: mapped to final Java class example enum PasswordList {pwd1, pwd2};

68 Java and CORBA (35) Application example: Steps implementation of IDL interface compilation using idltojava compilation of created Java classes using javac implementation of implementation classes creation of implementation server creation of client application start naming service tnameserv start server which is registered at naming service start client

69 IDL interface Java and CORBA (36) module AccountUpdate { }; //Update Account interface Functions { long updateaccount(in long number); };

70 Java and CORBA (37) Compilation of IDL file idltojava -fno-cpp AccountUpdate.idl -fno-cpp: switch off C/C++ preprocessor Compilation of Java classes javac AccountUpdate\*.java

71 Java and CORBA (38) Generation of implementation classes abstract file _FunctionsImplBase.java provide body for each interface method /* * File:./ACCOUNTUPDATE/FUNCTIONS.JAVA * From: ACCOUNTUPDATE.IDL * Date: Wed September 27 15:02: * By: idltojava Java IDL 1.2 Aug :25:34 */ package AccountUpdate; public interface Functions extends org.omg.corba.object, org.omg.corba.portable.idlentity { int updateaccount(int number); }

72 Java and CORBA (39) Implementation of interface //Implementation of Interface Functions.java import AccountUpdate.*; public class FunctionsImpl extends _FunctionsImplBase { } public FunctionsImpl() { } public int updateaccount(int number){ } //realize function here return 0;

73 Java and CORBA (40) Implementation of server component server class registers implemented object at ORB and Naming Service provides link to implementation class not created by idltojava!!

74 Java and CORBA (41) //Server-Class import AccountUpdate.*; import org.omg.cosnaming.*; import org.omg.cosnaming.namingcontextpackage.*; import org.omg.corba.*; public class Server { public static void main (String args[]){ try { //Creation of Server-ORB ORB orb = ORB.init(args, null); //create implementation object FunctionsImpl fimpl = new FunctionsImpl(); orb.connect(fimpl); //Handle for Name Server org.omg.corba.object oref = orb.resolve_initial_references ("NameService");

75 Java and CORBA (42) } } NamingContext nc = NamingContextHelper.narrow(oref); //Bind Object Reference NameComponent nco= new NameComponent("AC", ""); NameComponent path[]={nco}; nc.rebind(path, fimpl); //Await client calls java.lang.object sync = new java.lang.object(); synchronized (sync) { } sync.wait(); }catch (Exception e) { } System.err.println("Error: "+e);

76 Java and CORBA (43) Implementation of client component localizes reference to Functions object using naming service reference: CORBA reference which has to be narrowed to correct reference type name used by server: "AC"

77 Java and CORBA (44) //Client Class import AccountUpdate.*; import org.omg.cosnaming.*; import org.omg.corba.*; public class Client { public static void main (String args[]){ try { //Create Client-ORB ORB orb = ORB.init(args, null); //Create handle for Name Server org.omg.corba.object oref = orb.resolve_initial_references ("NameService"); NamingContext nc = NamingContextHelper.narrow(oref);

78 Java and CORBA (45) } } //Find Object Reference NameComponent nco= new NameComponent("AC", ""); NameComponent path[]={nco}; //Use helper class for casting Functions fun = FunctionsHelper.narrow(nc.resolve(path)); //call function int result = fun.updateaccount(444); }catch (Exception e) { } System.err.println("Error: "+e); e.printstacktrace();

79 Java and CORBA (46) Compilation of Java classes javac -d. FunctionsImpl.java Server.java Client.java Call naming service tnameserv tnameserv -ORBInitialPort 2000 returns Interoperable Object Reference (IOR) and port IOR can be used to localize CORBA object refs

80 Java and CORBA (47) Start client and server java Server -ORBInitialPort 2000 java Client -ORBInitialPort 2000

81 Jini (1) Introducing Jini infrastructure for distributed objects becoming "real" computers are inexpensive, small, and everywhere Jini: Goals enabling users to share services and resources over network providing users easy access to resources anywhere on the network while allowing the network location of the user to change simplifying the task of building, maintaining, and altering a network of devices, software, and users

82 Jini: Parts Jini (2) infrastructure: A set of components that provides an infrastructure for federating services in a distributed system. JVM, RMI, security, lookup programming model that supports and encourages production of reliable distributed services and events. Events, Leasing. services that can be made part of a federated Jini system and which offer functionality to any other members. Transactions, user defined (printing, storage,...)

83 Java and Jini Jini (3) Java Virtual Machine provides consistent processor Object Serialization allows objects to be sent via streams RMI allows objects to call objects on different processors and even transfer objects (proxies and dynamic downloading) Java security model allows fine grained control on what programs can do

84 Jini (4) Jini and distributed services discovery/join: Starting from scratch to join a group lookup leasing: Reserving a service for a set period of time events: sending events across processors transactions: Grouping a set of operations to one atomic operation service interfaces: Either standard or "homegrown"

85 Jini (5) Flow of typical interactions register a service ask for a lookup service (static port, or broadcast) lookup responds service joins the lookup service. Passes remote interface proxy use a service ask for a lookup service lookup responds query for a particular service, get proxy contact service using proxy (no more lookup service)

86 Jini details Jini (6) discovery uses IP broadcast to look for a Lookup service Lookup can handle name value pairs or list attributes service name, for example "bank name" service characteristics, for example printer: 1200 dpi, color,... Leases can be renewed if leasee needs more time RMI provides activation which helps recovering and starting services

87 Jini (7) Transaction service interface TransactionManager: Used for managers of the two-phase commit protocol for toplevel transactions abort (long id), commit (long id) create (long lease), join (long id, TransactionParticipant part, long crashcount) interface TransactionParticipant: Objects involved in a transaction abort (TransactionManager man, long id) commit(transactionmanager man, long id) prepare(transactionmanager man, long id)

88 Jini and CORBA Jini (8) CORBA defines IDL to create interfaces to objects. Subsequent objects can be implemented in any language. Jini is Java only. CORBA only supports passing primitive types, not objects such as Jini does. Version 2.2 of IIOP is supposed to support this. In general Jini shares capabilities with a CORBA system. They can communicate if needed.

89 Jini (9) Jini and Universal Plug and Play (UPnP) UPnP uses protocols, not passing object interfaces. UPnP addresses many of the same problems and has similar goals as Jini. Perhaps not as ambitious as Jini, UPnP will integrate well with Windows operating systems.

90 Jini and HP CHAI Jini (11) intelligent interaction with embedded devices uses Java within real-time environment ChaiVM goal: Universal Plug-and-Play change core Java to run in real-time similar approach like Jini

91 Jini issues Jini (12) Despite being a very dynamic system, Jini still requires static and well defined interfaces. Jini has many processes to configure and run (rmid, reggie, mahalo) Current lack of Integrated Development Evironments for doing Jini development Performance and bottlenecks. Current implementation can be slow. Lookup service could be a bottleneck. Too ambitious, not ambitious enough?

92 References S. Fischer and A. El Saddik. Open Java: Von den Grundlagen zu den Anwendungen. Springer Verlag, Heidelberg, 1999 (in German) H. Bader and W. Huber: Jini. Addison-Wesley, 1999 (in German) J.P. Redlich: CORBA2.0, Addison-Wesley, 1996 (in German) JavaSoft: Sun: Jini Community: Jini Corner: Chai: UPNP: Inferno: